1. Field of the Invention
The present invention relates to paper machines, and, more particularly, to paper machines including a deaerator for the fiber suspension which is connected to an inlet side of a headbox.
2. Description of the Related Art
A paper making-machine is used for making a fiber web from a fiber suspension. The fiber suspension is introduced into a headbox, such as a valley or a hydraulic headbox, at the wet end of the machine. The headbox discharges the fiber suspension with a particular cross-sectional profile onto a forming fabric on the wet end of the machine. The fiber suspension is typically in the form of fibers, such as wood fibers, which are suspended in water.
It is necessary to treat the fiber suspension which is introduced into the headbox such that the fiber web produced as the end product is of a particular quality with minimal defects. For example, the fiber suspension may be cleaned and bleached prior to introduction into the headbox. Another factor which tends to affect the quality of the fiber web is the inclusion of air in the fiber suspension as a result of various treating processes associated with the fiber suspension prior to being introduced into the headbox. Air within the fiber suspension is undesirable from a manufacturing and efficiency standpoint. For example, the air within the fiber suspension occupies a certain volume of the fiber suspension and interferes with drainage of the fiber suspension after being discharged from the headbox onto the forming fabric.
It is known to provide a deaeration unit which is connected to the inlet side of the headbox for the purpose of removing air from the fiber suspension. Such a deaeration unit typically is in the form of a large tank having a vacuum applied thereto using a vacuum source. An air space exists within the tank above the fiber suspension flowing therethrough. The vacuum within the tank causes the air bubbles within the fiber suspension to expand and rise to the top of the fiber suspension. The air bubbling to the top of the fiber suspension is drawn away from the tank using the vacuum source connected therewith.
A problem with a deaeration tank as described above is that only the top surface of the fiber suspension is exposed to the vacuum pressure. In other words, only a relatively small surface area of the fiber suspension when compared with the overall volume of the fiber suspension is directly exposed to the vacuum pressure. The efficiency of such a deaeration tank is therefore somewhat limited.
What is needed in the art is a deaeration unit which provides improved deaeration of the fiber suspension which is introduced into the headbox.